I think this service will be a big deal. After all the hoo-ha about privacy and nervousness about how people will use it dies down everyone will come to see that a service like this has real utility. New behavioural protocols will be required, and that will be uncomfortable to start with, but people will get over this, they always do. Look at telephones, mobiles, Facebook and now Twitter.
It doesn’t look like it has an API though. I hope one is coming as this would be a great tool for social networks like WAYN.